http static directories aren't being served

Your handler path (/css/) is passed to the FileServer handler plus the file after the prefix. That means when you visit http://myhost.fake/css/test.css your FileServer is trying to find the file ./css/css/test.css.

The http package provides the function StripPrefix to strip the /css/ prefix.

This should do it:

http.Handle("/css/", http.StripPrefix("/css/", http.FileServer(http.Dir("css"))))